It is a common practice to measure the capacitance of telephone cable pairs, the capacitance measurement being utilized primarily to identify and locate various types of telephone cable faults. The most commonly used apparatus for this purpose is of the Wheatstone bridge type. Such bridge apparatus has the disadvantages of requiring manual adjustment to balance for each measurement; the measured values must be manually modified by correction factors for cable pair lengths above 1/20 of the wave length of the test frequency; it is not effective to distinguish some faults for cable pair lengths approaching 1/4 of the test frequency wave length. Other types of available apparatus either are susceptible to errors due to interference (primarily from power lines) or have severe limitations due to non-linearity.
The general object of this invention is to provide improved method and apparatus for measuring the capacitance of telephone cable pairs.
More specifically, it is an object of the invention to provide method and apparatus for measuring the capacitance of telephone cable pairs, which apparatus has an output which is a linear function of the capacitance measured and has the property of substantially infinite rejection of a predetermined frequency and its harmonics, and yet which has requisite simplicity and economy.
For a further understanding of the invention and further objects, features, and advantages thereof, reference may now be had to the following description, taken in conjunction with the accompanying drawing.